Microstructure development in warm upset Electron Beam Melted Ti64

What is it about?

As AM Ti alloys generally contain porosity, for demanding applications it must be eliminated. HIP was reported, but it is expensive; accordingly forging by upsetting of EBM Ti6Al4V at 900°C was investigated. Strain rates of 0.01-1 s-1 were employed. In contrast to the as-printed material, porosity was not detected. From the plastometric tests the stress-true strain relationships were obtained and peak stresses were determined. Using the Simufact simulation program, details of the distribution of equivalent strains and temperatures were obtained. Comparison with wrought cast and printed materials is reported. The eventual microstructure consisted of alpha lamellae ranging in width from 1.81 to 2.34 μm, depending on strain rate and deformation, and beta formed in the interlamellar space during cooling in air. The hardness of the fully processed material was in the range of 293-304 HV1, independently of strain rate. This is to be compared with EBM Ti64, 316-360 HV0.3, and similarly processed cast wrought material, 350-365 HV0.3.

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Why is it important?

This work addresses the persistent challenge of porosity in additively manufactured Ti-6Al-4V (Ti64) alloys. While hot isostatic pressing (HIP) is the traditional method for eliminating porosity, it is expensive and not always accessible. Our research demonstrates that warm upsetting at 900 °C can effectively remove porosity from EBM-printed Ti64, producing a fine, homogeneous lamellar microstructure and mechanical properties comparable to those of conventionally forged or HIP-treated materials. By providing a cost-effective and scalable alternative to HIP, this study offers a timely contribution to the field, potentially expanding the industrial application of additively manufactured titanium alloys and increasing their reliability for demanding engineering uses.